1. Field of the Invention
The present invention is in the field of data-packet-telephony and pertains particularly to methods and apparatus for enabling controlled application of sealing current for twisted pair loops in data-network-telephony architectures.
2. Discussion of the State of the Art
In the field of telephony, copper line local loops described as those local loops that exist between a central office CO and customer premise equipment (CPE) in a given service area, require a sealing current to help maintain line integrity in reducing oxidation. A sealing current as defined in the Bell core and CCITT Layer 1 specifications is a low current (1-20 mA typically for POTS) direct current DC applied to a copper pair (loop) by a subscriber line interface circuit (SLIC) controlled by line usage by end devices. Sealing current is required to reduce oxidation at splice points and to aid in maintaining electrical integrity in the line.
In plain old telephony service (POTS), sealing current is applied when the telephone receiver is picked up or is “off hook”. A SLIC typically enables the alternate current states for the line and is controlled by the subscriber activity on the line. In POTS telephony, application of sealing current is efficient because the subscribers automatically control it or “cycle” it whenever they use the line and when the line is not used no sealing current is applied therefore, cost is proportional to line use.
More recently, with the advent of digital subscriber line (DSL) services, including ADSL (asynchronous) and VDSL (very high bit-rate), the network architecture is becoming more complex in terms of equipment used. One with skill in the art will appreciate that the ambiguity between pure digital network telephony architecture and POTS telephony architecture results from a fact that digital telephony equipment and lines and POTS equipment and lines are both in service with respect to a typical DSL network environment. State-of-art digital services are hybrid with existing public-switched-telephony-network (PSTN) services and rely still on much of the old architecture, largely for cost efficiency reasons. That is to say that it may be cost prohibitive for large companies owning their own PBX systems and the like to switch over to pure DNT network architecture. SLICs in the POTS architecture still control the application of sealing current for local loop integrity existent between a CO) and CPE.
In todays network environment some companies are providing IP telephony solutions such as wideband IP telephone systems. These hybridized systems are still interfaced with a traditional SLIC between CO and CPE equipment. Eventually typical POTS telephones and traditional SLICs will no longer be required or used in telecommunications networks as more and more subscribers opt for pure wireless and broadband telephony services. In some isolated networks, pure DSL-based service is available wherein no analog-type telephone systems are present. In these scenarios with no POTS telephones or SLICs, sealing current is applied as a constant current over all of the affected local wire loops between the CO and CPE.
Contemplating that there may be tens of thousands of local loops per typical CO, the prospect of providing a constant simultaneous current over that many loops in a pure digital network may be costly in terms of added equipment capacity required to generate the current. The implementation may also be somewhat compromised by arising thermal limitations for each of the current generating devices that must constantly generate the sealing current. It is also noted herein that VDSL, a higher rate broadband service, is now required for newer video services. VDSL implementation involves more outside-plant equipment, which is more sensitive to power consumption than normal thermal dissipation units.
Also in the above paragraph, we should note that higher rate broadband (VDSL) is required for newer video services and thus require more Outside Plant equipment that is much more sensitive the power consumption and thermal dissipation limits.
What is clearly needed in the art is a method and apparatus for controlling application of sealing current for maintaining integrity of local loops in a fashion that does not require constant current generation and delivery and without requiring POTS telephones to trigger application of the sealing current. Such a method and apparatus would enable pure DSL-based architectures to expand in a more cost efficient manner without requiring POTS integration and hybridization.